The present invention relates to a process for producing fluoropropenes in good yield on an industrial scale using commercially and readily available starting materials. More particularly, the present invention relates to a process for producing fluoropropenes by the dehydrohalogenation of halopropanes, either by reaction with an essentially miscible alkali or alkaline earth metal hydroxide solution in a non-alcohol solvent, or by thermal decomposition.
The production of fluoropropenes such as CF3CH═CH2 by catalytic vapor phase fluorination of various saturated and unsaturated halogen-containing C3 compounds is described in U.S. Pat. Nos. 2,889,379; 4,798,818 and 4,465,786. U.S. Pat. No. 5,532,419 discloses a vapor phase catalytic process for the preparation of fluoroalkene using a chloro- or bromo-halofluorocarbon and HF. EP 974,571 discloses the preparation of 1,1,1,3-tetrafluoropropene by contacting 1,1,1,3,3-pentafluoropropane (HFC-245fa) in the vapor phase with a chromium-based catalyst at elevated temperature, or in the liquid phase with an alcoholic solution of KOH, NaOH, Ca(OH)2 or Mg(OH)2.
A fluoropropene of particular interest is 1,3,3,3-tetrafluoropropene (HFC-1234ze), which has potential use as a low global warming potential refrigerant. However, this material is presently not available in commercial quantity. The existing technology to make HFC-1234ze is a fluorination process using 1,1,1,3,3-pentachloropropane (HCC-240fa) and HF in the presence of a vapor phase catalyst. HFC-1234ze is a by-product of the reaction that is made in relatively small quantity, i.e., less than about 8 area % in a gas chromatograph (GC) of the organic reaction product.
The process is very expensive because of the low selectivity for the desired product, HFC-1234ze. The reaction is actually intended for the manufacture of HFC-245fa, in which small quantities of HFC-1234ze is produced as a by-product. Complicating matters, the process involves handling large quantities of hazardous materials such as HF and HCl.
Henne et al., J. Am. Chem. Soc., 68, 496–497 (1946) described the synthesis of various fluoropropenes from CF3CH2CF3 using, e.g., alcoholic KOH, with varying degrees of success. For example, it is stated that in some instances dehydrohalogenation was unsuccessful. In another instance, a protracted reaction time (3 days) was required, or relatively low product yield (40%, 65%) was obtained.
Tarrant, et al., J. Am. Chem. Soc., 77, 2783–2786 (1955) described the synthesis of CF3CH═CF2 starting with: (1) 3-bromo-1,1,3,3-pentafluoropropane and reacting it with a hot solution of KOH in water; and (2) 3-bromo-1,1,3,3-tetrafluoropropene, reacting it with HF at 150□C and neutralizing the reaction products with a KOH solution.
Kimura, et al., J. Org. Chem. 48, 195–198 (1983) described multi-phase dehydrohalogenation of brominated compounds using aqueous KOH and a phase transfer catalyst based on polyethylene glycols and polyethylene glycol-grafted copolymers. The preparation of fluoropropenes by the dehydrohalogenation of fluoropropane using aqueous KOH and a phase transfer catalyst, but with improved yields and selectivity is disclosed by U.S. Pat. No. 6,548,719.
There is a continuing need for means by which fluoropropenes can be produced commercially with high yield and selectivity, either catalytically or non-catalytically.